The technology of the present disclosure relates generally to distributed antenna systems (DASs) that support distributing communications services to remote units, and particularly to per band gain control of remote uplink paths in remote units.
Wireless communication is rapidly growing, with ever-increasing demands for high-speed mobile data communication. As an example, local area wireless services (e.g., so-called “wireless fidelity” or “WiFi” systems) and wide area wireless services are being deployed in many different types of areas (e.g., coffee shops, airports, libraries, etc.). Distributed communications or antenna systems communicate with wireless devices called “clients,” “client devices,” or “wireless client devices,” which must reside within the wireless range or “cell coverage area” in order to communicate with an access point device. Distributed antenna systems are particularly useful to be deployed inside buildings or other indoor environments where client devices may not otherwise be able to effectively receive radio-frequency (RF) signals from a source, such as a base station for example. Example applications where distributed antenna systems can be used to provide or enhance coverage for wireless services include public safety, cellular telephony, wireless local access networks (LANs), location tracking, and medical telemetry inside buildings and over campuses.
One approach to deploying a distributed antenna system involves the use of RF antenna coverage areas, also referred to as “antenna coverage areas.” Antenna coverage areas can be formed by remotely distributed antenna units, also referred to as remote units (RUs). The remote units each contain or are configured to couple to one or more antennas configured to support the desired frequency(ies) or polarization to provide the antenna coverage areas. Antenna coverage areas can have a radius in the range from a few meters up to twenty meters as an example. Combining a number of remote units creates an array of antenna coverage areas. Because the antenna coverage areas each cover small areas, there typically may be only a few users (clients) per antenna coverage area. This arrangement generates a uniform high quality signal enabling high throughput supporting the required capacity for the wireless system users.
As an example, FIG. 1 illustrates distribution of communications services to coverage areas 10(1)-10(N) of a DAS 12, wherein ‘N’ is the number of coverage areas. These communications services can include cellular services, wireless services such as RFID tracking, Wireless Fidelity (WiFi), local area network (LAN), WLAN, and combinations thereof, as examples. The coverage areas 10(1)-10(N) may be remotely located. In this regard, the remote coverage areas 10(1)-10(N) are created by and centered on remote antenna units 14(1)-14(N) connected to a central unit 16 (e.g., a head-end controller or head-end unit). The central unit 16 may be communicatively coupled to a base station 18. In this regard, the central unit 16 receives downlink communications signals 20D from the base station 18 to be distributed to the remote antenna units 14(1)-14(N). The remote antenna units 14(1)-14(N) are configured to receive downlink communications signals 20D from the central unit 16 over a communications medium 22 to be distributed as downlink communications signals 20D to the respective coverage areas 10(1)-10(N) of the remote antenna units 14(1)-14(N). Each remote antenna unit 14(1)-14(N) may include an RF transmitter/receiver (not shown) and a respective antenna 24(1)-24(N) operably connected to the RF transmitter/receiver to wirelessly distribute the communications services to client devices 26 within their respective coverage areas 10(1)-10(N). The size of a given coverage area 10(1)-10(N) is determined by the amount of RF power transmitted by the respective remote antenna unit 14(1)-14(N), the receiver sensitivity, antenna gain and the RF environment, as well as by the RF transmitter/receiver sensitivity of the client device 26. Client devices 26 usually have a fixed RF receiver sensitivity, so that the above-mentioned properties of the remote antenna units 14(1)-14(N) mainly determine the size of their respective remote coverage areas 10(1)-10(N).
In the DAS 12 in FIG. 1, the remote antenna units 14(1)-14(N) are also configured to receive uplink communications signals 20U from the client devices 26 in their respective coverage areas 10(1)-10(N). The uplink communications signals 20U may be received in multiple frequency bands. The uplink communications signals 20U received in multiple frequency bands can be routed to different uplink path circuits (not shown) in the remote units 14(1)-14(N) related to their frequency band. At the related uplink path circuits in the remote units 14(1)-14(N), the uplink communications signals 20U can be filtered, amplified, and combined together into the combined uplink communications signals 20U to be distributed to the central unit 16. If the input power of one of the frequency bands of the received uplink communications signals 20U in a given remote unit 14 is PI, the final uplink power level PL of the signal is given by PL=PI+GR+GH, where GR is the gain in the remote unit 14 from its antenna 24 to the signal combination point and GH is the gain in the head-end unit. In this case, GR+GH is referred to as the end-to-end gain.
In the DAS 12 in FIG. 1, the gain GR of a remote unit 14 determines the sensitivity of the remote unit 14. Higher gain provides higher sensitivity (i.e., increased ability to decode weak uplink communications signals 20U). In this regard, each remote antenna unit 14(1)-14(N) in the DAS 12 in FIG. 1 may include automatic level controllers (ALCs) 28(1)-28(N) that limit the power level of the received incoming uplink communications signals 20U to a predetermined power level. The ALCs 28(1)-28(N) can be used in the remote antenna units 14(1)-14(N) to avoid strong incoming uplink communications signals 20U overloading the communications signal processing circuitry (e.g., an amplifier) and distorting the uplink communications signal 20U. As another example, if the DAS 12 is an optical fiber-based DAS in which the remote antenna units 14(1)-14(N) convert the uplink communications signal 20U to optical uplink signals, a strong uplink communications signal 20U could overload the laser diode (not shown) used to convert the uplink communications signal 20U to optical uplink signals.
It may be important that the combined uplink power of the combined uplink communications signals 20U remain below a combined uplink power level threshold. For example, if the DAS 12 in FIG. 1 is an optical fiber-based DAS, the signal combination point may be a laser diode to convert the combined uplink communications signals 20U to an optical signal. The laser diode enters into a non-linear region above a defined power level. Since which remote units 14(1)-14(N) may receive a high power signal is not known beforehand, the system must prepare for a worst case power level scenario where each of the remote units 14(1)-14(N) is assumed to receive a high power signal. To ensure the remote units 14(1)-14(N) can handle such a worst case power level scenario, the gain GR of the remote units 14(1)-14(N) needs to be set to a very low value in order to maintain the combined uplink power level at or below the combined power level threshold. This creates a dilemma. If the uplink power level of the combined uplink communications signals 20U of a remote unit 14 is below the combined uplink power level threshold at any given time, the gain GR of the remote unit 14 will be lower than it could otherwise be with the combined uplink power level still not exceeding the combined uplink power level threshold. Thus, the sensitivity of the remote unit 14 will be less than it could otherwise be if a lower combined uplink power level of the combined uplink communications signals 20U were assumed. However, if the gain GR of the remote unit 14 were set assuming a lower combined uplink power level of the combined uplink communications signals 20U, there will be times when the combined uplink power level of the combined uplink communications signals 20U is higher thus causing the combined uplink power level to exceed the combined uplink power level threshold for the remote unit 14.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.